For everyone who is concerned about government subsidies for solar power, it should be remembered that electrification of rural America was only possible with substantial subsidies. One of your great presidents, Lyndon Johnson, was responsible for much of this. The gain in agricultural performance and human capital dwarfs the cost of the subsidies. Local generation of power will in the long run have significant effect on the capital requirements and electrical losses in the Grid, as well as providing redundancy during outages. .

I am also an EE that installed a 2.5Kw system at my recreational cabin about 8 years ago. I am off-grid, so, payback is not the issue.. Two things I would like to add to your payback calculations. The cost of electricity is continually rising which will shorten the payback period. The second item is that you have actually made a capital investment, which means that you have increased the value of your property by the value of the investment minus depreciation.

The calculations for energy useage are as follows:Heat of vaporization of water is 970 BTU/pound. To raise the water from 42 degrees to 212 will require an additional 170 BTU. 1140 BTUs is equal to 0.33 KWh, so to boil a gallon of water (i.e. about 10 pounds) requires about 3.3 KWh.This is assuming 100% efficiency. The device described would probably be only about 10% efficient, but a properly designed still would probably be about 80% efficient. (Start with an immersion heater in an insulated container, and use air or a water filled heat sink for condensing).